The invention is based on a friction brake for braking a vehicle equipped with at least one friction brake as described hereinafter.
Such a friction brake in the form of a disk brake is already known (German DE 40 21 572 A1), in which an electric motor acts as the drive source for the clamping device. Its motor shaft is connected by a non-shiftable coupling to a worm of a worm gear whose worm wheel is seated on a recirculating ball screw that indirectly engages the piston of the clamping device. The clamping power for this friction brake must therefore be provided solely by the electric motor. Because limited space is available for it inside the wheel rim of the vehicle wheel, only a relatively small electric motor can be used. For a motor with limited capacity to generate the necessary clamping power, the worm gear must have a high transmission ratio. As a consequence, the brake reacts relatively sluggishly to braking signals. Although it would be possible to increase the dynamics of the friction brake by putting a higher load on the electric motor, this would result in negative repercussions on the electrical system of the vehicle. Moreover, a considerable disadvantage is the self-locking action of the worm gear, so that an electric motor is also required to release the brake. A non-self-releasing brake, however, represents a potentially serious danger.
It is further known (EP 0 177 767 A1) to provide vehicles with a hydraulic deceleration device triggered by the driver in the form of a service brake. In this case, a positive displacement pump is used that is disposed in a wheel hub, on the delivery side of which a device for generating a counterpressure is positioned, and a cooling device is downstream of the device. The pump can have an adjustable volumetric displacement and be triggered by a servo motor. Such a brake has limited dynamics. Moreover, the hydraulic deceleration device is also subject to losses in the non-braking state. In addition, the cooling device requires a great deal of space.